1. Field of the Invention
The present invention relates to a method for molding a magnetic tape cassette such as a video tape cassette and the like, and more particularly, for molding guide walls of a brake member, in the magnetic tape cassette, which prevents a magnetic tape from loosening. In addition, the present invention relates to an apparatus in which the above-mentioned molding method is operable.
2. Description of the Related Art
Conventionally, there are known various types of magnetic tape cassettes that can be used in a video deck. As an example of the magnetic tape cassettes, there are relatively small-sized magnetic tape cassettes used in a digital video cassette (DVC).
FIG. 4 is an exploded view of a general magnetic tape cassette 30 that is structured in the following manner. A pair of reels 32a and 32b is rotatably disposed on a lower half-case 31 (hereinafter referred to as xe2x80x9clower halfxe2x80x9d). Around the two reels 32a and 32b, a magnetic tape T (not shown in FIG. 4) is wound. The magnetic tape T is guided by two tape guides 33a and 33b located at the right and left sides of the front end of the cassette 30. The two tape guides 33a and 33b allow the magnetic tape to pass through an opening 34 formed on the front end side of the lower half 31. As shown in FIG. 4, teeth 35a and 35b are formed along the entire peripheral edges of the lower flanges 32La and 32Lb of the two reels 32a and 32b. 
As also shown in FIG. 4, a brake member 38 is provided between the two reels 32a and 32b in a space 36 located on the rear side of the lower half 31. The brake member 38 prevents the magnetic tape T from loosening when the magnetic tape cassette 30 is not loaded in a video deck (not shown), but is instead located in a storage place or is being carried.
A pair of securing pawls 37a and 37b is provided near the front end of the brake member 38. The securing pawls 37a and 37b form a lock member to lock the rotation of the reels 32a and 32b together with the brake member 38. In addition, a compression spring (brake spring) 39 is provided at the rear end of the brake member 38 in the lower half-case 31. The compression spring is used to urge the brake member 38 towards the front side of the lower half-case 31.
As shown in FIG. 4, an upper half-case 40 (hereinafter referred to as xe2x80x9cupper halfxe2x80x9d) cooperates with the lower half 31 to form the magnetic tape cassette 30. The upper half 40 includes a lid for covering the opening in the front end portion of the lower half 31. The lid is composed of an outer lid 41, an upper lid 42, and an inner lid 43. The opening can be freely opened and closed using these lids.
The outer lid 41 of the upper half 40 includes a side plate 44 having a projecting lock pin 45. Correspondingly, a lid lock 47, which is rotatably mounted on one side plate 46 of the lower half 31, locks the outer lid 41 of the upper half 40 by engaging with the lock pin 45. A plate spring 48 urges the lid lock 47 toward the locking side thereof.
As shown in FIG. 4, a rotary shaft 44b projects from an inner side of the side plate 44 of the outer lid 41. A lid spring 49, which is mounted on the rotary shaft 44b, is used to open and close the outer lid 41. In FIG. 4, reference numerals of components other than main components of the magnetic tape cassette 30 are omitted, since descriptions thereof are not believed to be essential for an understanding of the general cassette 30.
FIG. 5 shows a conventional lock device for locking the rotation of the reels 32a and 32b of the general magnetic tape cassette 30 described above with reference to FIG. 4. In the conventional lock device, the brake member 38 is urged in the forward direction, which is the direction in which the compression spring 39 (brake spring) is compressed. The compression spring 39 is supported along the floor surface 31a of the lower half 31 shown in FIG. 4, and has one end engaged with the floor surface 31a and the other end engaged with the rear end of the brake member 38. The compression spring 39 urges the brake member 38 in the forward direction when the cassette 30 is not loaded in a video deck. An insertion hole 51 is formed substantially in the central portion of the bottom surface 38a of the brake member 38. A lock release pin of the video deck (not shown) is inserted into the insertion hole 51 of the brake member 38 when the magnetic tape cassette 30 is loaded in a video deck, thereby allowing the reels 32a and 32b to rotate.
A pair of guide walls 52a and 52b is provided on the left and right positions of the insertion hole 51, and slidingly guides movement of the brake member 38. Facing brake member removal-prevention projections 53a and 53b are provided on the upper ends of the two guide walls 52a and 52b so as to prevent the brake member 38 from being removed from the cassette 30.
As described above, the two guide walls 52a and 52b are conventionally provided on the left and right sides of the brake member 38. The two guide walls 52a and 52b are located to the left and right of the insertion hole 51 because it is necessary to facilitate the removal of molds employed in a resin injection-molding method. FIG. 6 is a cross-sectional view of a metal mold 120 used for explaining the conventional molding method. The metal mold 120 is used to mold the lower half 31 of the cassette 30, and is composed of an upper mold UM and a lower mold LM. The lower mold LM has a component mold CM for molding inner surfaces of the guide walls 52a and 52b. As shown in FIGS. 5 and 6, if the two guide walls 52a and 52b are erected on the lower half 31 and are disposed adjacent to the insertion hole 51, the component mold CM may be easily removed in the direction L6 after completion of the injection-molding.
However, the location of the pair of guide walls 52a and 52b has drawbacks in that the brake member removal-prevention projections 53a and 53b, which are provided on the upper ends of the guide walls 52a and 52b, do not sufficiently hold the brake member 38. In other words, the pair of guide walls 52a and 52b holds only the substantially central portion of the brake member 38. As a result, the brake member 38 can fly out or slip off from the two guide walls 52a and 52b due to the urging force of the compression spring 39 in the assembled magnetic tape cassette.
In view of the above-described drawback, it is preferable to support the brake member 38 using two or more pairs of guide walls respectively with brake member removal-prevention projections that are the similar to those identified with reference numerals 53a and 53b. For example, as shown in FIG. 2, if two pairs of guide walls have brake member removal-prevention projections, the brake member 38 can be supported in both the front and rear end portions. However, such an arrangement requires that the two pairs of guide walls should be located far from the is insertion hole 51.
Moreover, the conventional apparatus and methods cannot be used to injection-mold such a two-pair structure because the component mold CM exists between the two guide walls 52a and 52b. As described above, the component mold CM is conventionally removed from the insertion hole 51 in the direction L6, as shown in FIG. 6. Therefore, the component mold CM cannot be removed because the brake member removal-prevention projections 53a and 53b mutually overhang and prevent the component mold CM from being removed in the direction L6.
It is an object of the present invention to overcome the above-mentioned drawbacks found in the conventional magnetic tape cassette molding method and apparatus. That is, it is an object of the present invention to provide a magnetic tape cassette molding method that more easily molds guide walls for holding a brake member.
A further object of the present invention is to provide an apparatus for performing the above method.
The above object can be attained by a mold apparatus for injection-molding a magnetic tape cassette having a pair of mutually opposing guide walls respectively erected on an upper surface of a half-case of the magnetic tape cassette. The opposing guide walls slidably support a brake member that locks rotations of a pair of tape winding reels disposed within the magnetic tape cassette. Each of the guide walls has a projection for preventing the brake member from being dislodged from between the guide walls. The mold apparatus comprises a first mold, a second mold and a third mold. The first mold, which is removable in a direction that is opposite the erected direction of the guide walls, forms a lower surface of the half-case. The second mold, which is removable in the erected direction of the guide walls, forms outer side surfaces of the guide walls. The third mold, which is removable in the erected direction of the guide walls, forms inner side surfaces of the guide walls that are brought into contact with the brake member. The third mold includes grooved portions respectively forming the projections of the guide walls. When assembled, the first, second and third molds form a molding cavity defined by the pair of mutually opposing guide walls.
In the above-mentioned construction, it is preferable that the projections of the apparatus are respectively positioned at leading ends of the guide walls.
Each of the projections of the apparatus, whether or not the projections of the apparatus are respectively positioned at leading ends of the guide walls, may have a surface that curved in cross section.
At least two pairs of the guide walls of the apparatus, whether or not the projections of the apparatus are respectively positioned at leading ends of the guide walls, are arranged at a predetermined interval in a sliding direction of the brake member.
Further, in accordance with the present invention, there is provided a method for injection-molding a magnetic tape cassette using a molding apparatus such as the one described immediately above. The method comprises the steps of forming a molding cavity using first, second and third molds such as the ones described above, molding molten resin into the molding cavity so as to form the mutually opposing guide walls, and then removing the second and third molds. The second mold is removed first, in the erected direction of the guide walls, so as to release the second mold from the molded guide walls. The third mold is then removed in the erected direction of the guide walls, while a distance between the projections formed on the guide walls is enlarged due to elastic deformation of the guide walls resulting from contact between the third mold and the projections formed on the guide walls.
In addition, the method may further comprise the step of guiding the removal of the third mold using the projections, wherein each of the projections has a surface that is curved in cross section.